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“Petit cosmetic surgery,” as hyaluronic acid injection is called for its ease, has spread explosively as aesthetic medicine without a scalpel.
But contrary to that easy-sounding name, blood vessels, the “lifelines,” run intricately under the skin, and once an accident occurs, the effects can reach the eyes and even the brain.
Almost two years have passed since our previous article in 2024.
In fact, I was surprised to examine several patients with skin embolism after hyaluronic acid filler injection.
In this short period, findings that require us to revisit conventional wisdom have been reported one after another: a strict recommendation from the American Academy of Ophthalmology (AAO), large-scale epidemiological data from Japan, and a startling fact showing a link with the “brain.”
In this article, based on evidence as of 2025, I explain in detail the “true risks” of hyaluronic acid injection and new findings, including an innovative technology from Japan.
Why does it get “blocked”? The pitfall of blind technique
First of all, why does hyaluronic acid block blood vessels?
To understand the mechanism, you need to understand that this procedure is basically a “blind” technique.
Invisible vessels and the fear of “backflow”
The physician inserts a needle through the skin, but cannot see through to the exact position of the blood vessels under the skin.
What happens if the needle tip happens to enter an artery (such as the facial artery or supraorbital artery) and hyaluronic acid is pushed out under high injection pressure?
- Retrograde embolism: strong pressure makes the hyaluronic acid flow backward in the artery against the bloodstream.¹
- And to the eye: the moment the injection stops, the hyaluronic acid is swept along at once by blood pressure from the heart, flows into the arteries of the eye (such as the central retinal artery), and blocks the vessel.
This is the cause of sudden loss of vision in the “eye,” far from the injection site.
It is called central retinal artery occlusion (CRAO) and is one of the most feared conditions among ophthalmic emergencies.
Is “cannulas are safe” a myth?
You may have heard the explanation that “if a blunt-tipped cannula (blunt needle) is used, it won’t pierce a vessel, so it is safe.”
It is true that the risk is said to be lower than with a sharp needle, but it cannot be said that “cannulas are absolutely safe,” and no such guarantee has been obtained at present.
Reports in 2025 point out that even a cannula can perforate a vessel if pushed with excessive force,
and that especially in wide areas such as the forehead, the tip of a long cannula is hard to control and there is a risk that it strays into a vessel without anyone noticing.²
“Cerebro-ocular ischemic syndrome”: the eye is an outpost of the brain
Until now, trouble from hyaluronic acid has tended to be seen as separate problems by site, such as “skin rotting (skin necrosis)” or “vision dropping.”
But new findings redefine this as a broader condition called“cerebro-ocular ischemic syndrome.”
Hidden “multiple” cerebral infarcts were present
The arteries of the eye branch off from the “internal carotid artery” that continues to the brain.
In other words, if filler has flowed back to the arteries of the eye, it would not be surprising if it also spread to the blood vessels of the brain just beyond.
In a case series by Zhao et al. (2024), of 12 patients who developed serious vascular complications after filler injection, about 42% (5 cases) of those who underwent brain MRI had multiple cerebral infarcts, most of them in the watershed areas of the frontal and parietal lobes.³
These cerebral infarcts are often asymptomatic (silent strokes), but in 3 of the 5 confirmed cases they were accompanied by obvious stroke symptoms such as paralysis of the limbs.³
Symptoms such as “eye pain” and “blurred vision” may be a sign of cerebral infarction, or a sign that a cerebral infarct has already occurred.
Largest-scale data from Japan show the danger of the “forehead”
In Europe and the United States, injection into the “nose” is considered most dangerous.
But this may not apply to us Japanese.
In a large survey published by Tamura et al. in 2025, covering about 300,000 injections, 80% (8 cases) of the 10 cases of vascular occlusion occurred in the “forehead.”¹
Only one case each occurred at the nose and the nasolabial fold.
Japanese people tend to prefer a rounded forehead, and the injected volume tends to be large.
Those considering injection into the forehead need to understand this “risk specific to Japanese people” sufficiently and decide carefully.
The reality of treatment is harsh: a warning from the AAO
If an accident happens, is there a treatment?
For many years it was believed that “injecting hyaluronidase (a dissolving enzyme) behind the eye (retrobulbar) would improve it.”
But the conclusion published by the American Academy of Ophthalmology (AAO) in March 2025 was extremely severe.
“There is little evidence supporting the effectiveness of treatment for improving vision loss.”² ⁴。
In animal experiments too, the majority of results show that an enzyme injected from outside a vessel cannot penetrate the arterial wall and dissolve the blockage inside.⁵
In current standard treatment, injecting hyaluronidase into the skin is essential to prevent skin necrosis, but the reality is that no reliable method has been established to restore vision once lost.
“EYE-CODE,” a global-language protocol for emergencies
A 2025 paper proposed a protocol, “EYE-CODE,” to let doctors other than ophthalmologists respond to the acute phase accurately without panicking.⁶
- E (Evaluate & EMS): evaluation and emergency call
First check vision and call an ambulance (119) immediately. Report it as a “suspected stroke” and request transport to a specialist hospital. - Y (Yell/Call): contact a specialist
Contact a nearby partner ophthalmologist or a core hospital. - E (Eye Pressure): lower eye pressure
Lower the eye pressure with eye drops or an intravenous drip to encourage recovery of blood flow. - C (Consume/Chew): take aspirin
If possible, chew and take aspirin to thin the blood and prevent the clot from worsening. - O (Oxygen & Ocular Massage): oxygen and massage
Give oxygen and perform eyeball massage to try to move the embolus in the vessel. - D (Dissolve): dissolution (local)
This is very important. To prevent necrosis of the skin and subcutaneous tissue, inject a sufficient amount of hyaluronidase (dissolving enzyme) into the injection site (such as the forehead or nose). - E (Embolism Team): hand-over to a specialist team
Finally, hand the patient over to a specialized facility capable of hyperbaric oxygen therapy and the like.
This “EYE-CODE” is a guidepost so that doctors can act without hesitation.
At the clinic where you will have a procedure, asking “Doctor, have you decided on an emergency response procedure such as ‘EYE-CODE’?” may be one way to check safety.
Possibilities and current challenges of robot-assisted surgery
While the severe situation continues, new treatment options are beginning to be shown from Japan to the world.
This is an innovative technique called “robot-assisted retinal artery cannulation,” developed by Professor Kazuaki Kadonosono of Yokohama City University and colleagues.⁷
Inserting a needle into a vessel 0.1 mm in diameter
This is an extremely advanced surgery in which a surgical-assist robot eliminates hand tremor completely and a needle thinner than a hair is inserted directly into the central retinal artery of the fundus, only about 100 μm (0.1 mm) in diameter, to inject a drug.
- High success rate:
In treating central retinal artery occlusion (CRAO) caused by thrombus, a high recanalization rate of 76.9% and improvement in vision have been reported. - Direct dissolution:
Because hyaluronidase can be poured directly into the vessel rather than from outside it, in theory it can dissolve the blockage most reliably.
To avoid any misunderstanding, however, this must never be taken to mean that “it is fine even if the procedure goes wrong.”
Professor Kazuaki Kadonosono is one of the most respected physicians in the entire ophthalmology community.
This technology is currently an advanced medical technique studied mainly for thrombotic disease, and it is not generally established as emergency treatment for cosmetic medicine complications.
Please understand that we cannot rely on a casual idea such as “we can leave it to robot surgery in an emergency,” and that it remains only a possible future “last resort.”
Finally: to receive aesthetic medicine safely
- Hyaluronic acid injection is called “petit cosmetic surgery,” but the risk is by no means “petit.”
- Japanese people in particular need to be careful about injection into the “forehead.”
- Know the limits of the “blind technique,” and remember that in an emergency, a response in line with that for “stroke” is necessary.
- It is also important to check whether the doctor has emergency preparedness, such as the emergency response protocol “EYE-CODE”⁶.
I have written this not to stir up anxiety.
Understanding the risks correctly is the most important means of protecting yourself.
Please choose a reliable doctor and make a point of receiving treatment with safety in mind.
References
- Tamura T, Tamura T, Okumura K, Funakoshi Y, Teranishi H. Serious Complications of Hyaluronic Acid Fillers-A Retrospective Study of 290,307 Cases. Ann Plast Surg. 2025;94(6):630-633. doi:10.1097/SAP.0000000000004327 https://pubmed.ncbi.nlm.nih.gov/40358958/
- Foster J, Aakalu VK, Freitag SK, et al. Vision-Threatening Complications of Soft Tissue Fillers: A Report by the American Academy of Ophthalmology. Ophthalmology. 2025;132(8):935-944. doi:10.1016/j.ophtha.2025.01.020 https://pubmed.ncbi.nlm.nih.gov/40167411/
- Zhao F, Chen Y, He D, You X, Xu Y. Disastrous cerebral and ocular vascular complications after cosmetic facial filler injections: a retrospective case series study. Sci Rep. 2024;14(1):3495. Published 2024 Feb 12. doi:10.1038/s41598-024-54202-w https://pubmed.ncbi.nlm.nih.gov/38347086/
- Foster J, Aakalu VK, Freitag SK, et al. Vision-Threatening Complications of Soft Tissue Fillers: A Report by the American Academy of Ophthalmology. Ophthalmology. 2025;132(8):935-944. doi:10.1016/j.ophtha.2025.01.020 https://pubmed.ncbi.nlm.nih.gov/40167411/
- Madala S, Davuluru S, Li J, et al. Management of vision loss associated with complications of cosmetic filler injections. Front Ophthalmol (Lausanne). 2025;5:1568370. Published 2025 Apr 11. doi:10.3389/fopht.2025.1568370 https://pubmed.ncbi.nlm.nih.gov/40291837/
- Barbarino S, Khalifian S, Fezza J. EYE-CODE Protocol for the Nonophthalmologist for Treatment of Retinal Artery Occlusion After Intra-Arterial Injection of Soft-Tissue Fillers: 2025 Update. J Cosmet Dermatol. 2025;24(7):e70336. doi:10.1111/jocd.70336 https://pubmed.ncbi.nlm.nih.gov/40631662/
- Kadonosono K, Yamane S, Inoue M, Yamakawa T, Uchio E. Intra-retinal Arterial Cannulation using a Microneedle for Central Retinal Artery Occlusion. Sci Rep. 2018;8(1):1360. Published 2018 Jan 22. doi:10.1038/s41598-018-19747-7 https://pubmed.ncbi.nlm.nih.gov/29358594/
